Option-1 : Hard Reset OPPO A7 with software menu

1. Turn on the OPPO A7
2. Make sure the battery is not empty
3. Backup important data at OPPO A7 because all data and applications will be erase or delete
4. Go to Menu :  Setting 
5. Choose Tab : General
6. Press Backup & Reset > Restore factory setting
7. Better you not check anything at the option if you do not want to erase data at data partition at internal memory
8. Choose Reset phone 
9. The OPPO A7 will do the master reset process.

Option-2 : Hard Reset OPPO A7 Factory Default using Hardware Secret Button Key

If we can not go to menu, or OPPO A7 can not turn on or hang or stuck or frozen so we can not access the menu setting or nothing happen while touch the screen, then try to factory reset with secret button and hardware key

1. Turn off the OPPO A7
2. Make sure the battery OPPO A7 already full or more than 50%
3. Press together and hold the Power Button + Volume Down Button
4. If the Logo appear, then release the button, after that we will enter some menu
5. Choose wipe data / factory reset using Volume Button, and press Power Button to Enter or OK
6. The OPPO A7 will continue master reset, wait for several minutes until OPPO A7 start like new again.